1. Field of the Invention
The invention relates to a manufacturing method of a liquid crystal display device and a liquid crystal panel base material.
2. Description of the Related Art
TN (Twist Nematic) mode liquid crystal display devices in which a liquid crystal material having positive dielectric anisotropy is oriented so as to be parallel to a substrate plane and be twisted by 90 degrees between opposing substrates have been widely used as active matrix type liquid crystal display devices. The TN mode liquid crystal display devices, however, have relatively poor viewing-angle characteristics, and various methods have therefore been developed in order to improve the viewing-angle characteristics.
For example, so-called ASV (Advanced Super View) mode liquid crystal display devices have been developed as a method for improving viewing-angle characteristics. In the ASV-mode liquid crystal display devices, a liquid crystal material having negative dielectric anisotropy is oriented perpendicular to a substrate plane, and the viewing-angle characteristics are improved by using rivets and electrode slits and the like formed in the inner surfaces of the substrates.
The ASV mode can improve the viewing-angle characteristics of liquid crystal display devices. In this mode, however, response of liquid crystal molecules is obtained by an oblique electric field effect provided by the rivets and the electrode slits. The liquid crystal molecules near the substrate surfaces, rivets, and electrode slits therefore have a high response speed, while the other liquid crystal molecules, especially those located in an intermediate part of a liquid crystal layer, have a low response speed. The reason for this is as follows: since an alignment film is formed on the substrate surfaces, rivets, and electrode slits, an excellent pretilt angle is applied to the liquid crystal molecules near the substrate surfaces, rivets, and electrode slits by the alignment film. However, an excellent pretilt angle is not applied to the liquid crystal molecules located away from the alignment film. It is therefore difficult to sufficiently increase the response speed of the liquid crystal molecules in moving image display, and technology for improving the response speed of liquid crystal molecules has been demanded.
A method using polymer stabilization technology has been proposed as technology of improving the response speed in the ASV mode. In the polymer stabilization technology, a mixture of liquid crystal and a monomer as an additive is injected between substrates, and the monomer is polymerized and altered with liquid crystal molecules oriented to a predetermined direction. A polymer that adsorbs the liquid crystal molecules is thus produced. An excellent pretilt angle can be applied to the liquid crystal molecules in the whole liquid crystal layer by adsorptive power of this polymer. Orientation regulation force to the liquid crystal molecules can thus be improved, whereby the response speed of a liquid crystal display device can be improved.
Technology using such polymer stabilization technology is disclosed in, for example, Patent document 1. A liquid crystal display device disclosed in Patent document 1 has, in a liquid crystal layer, a hardened material (polymer) having a liquid crystal framework that tilts liquid crystal molecules. An excellent pretilt angle can be given to the liquid crystal molecules by adsorptive power of the liquid crystal framework. As a result, response characteristics of the liquid crystal molecules to voltage application can be improved.
When this liquid crystal display device is manufactured, a bonded substrate is first divided into individual cells, whereby individual liquid crystal panels are obtained. Next, a liquid crystal material and a photopolymerizable resin material are injected into each liquid crystal panel. A voltage is then applied to the liquid crystal panel to orient liquid crystal molecules to a predetermined direction. In this state, ultraviolet (UV) rays are emitted to the liquid crystal panel to polymerize the photopolymerizable resin.
In a conventional liquid crystal panel fabrication process, on the other hand, a first substrate that is a collection of TFT substrates and a second substrate that is a collection of counter substrates are bonded to each other to form a bonded substrate. The bonded substrate is then separated into individual liquid crystal panels by a dividing process or the like, and a liquid crystal material is injected into each liquid crystal panel. However, a liquid crystal dropping/bonding process has been proposed and used in practical applications in order to improve productivity and to reduce loss of a liquid crystal material.
In a commonly used liquid crystal dropping/bonding process, a sealant is drawn on one of a first substrate and a second substrate, and liquid crystal is dropped. The sealant is then cured by emitting UV rays, whereby the first substrate and the second substrate are bonded to each other.
When a liquid crystal panel is manufactured by using a liquid crystal dropping/bonding process and polymer stabilization technology, a sealant is first drawn on a first substrate or a second substrate. A liquid mixture of a liquid crystal material and a photopolymerizable resin material is then dropped onto the substrate having the sealant drawn thereon, and the first substrate and the second substrate are bonded to each other to form a bonded substrate. The sealant is then cured by emitting UV rays to the bonded substrate. Thereafter, the bonded substrate is separated into individual liquid crystal panels by dividing the bonded structure. Liquid crystal molecules are oriented to a predetermined direction by applying a voltage to each of the divided individual liquid crystal panels, and the photopolymerizable resin material in the liquid crystal layer is polymerized and altered by emitting UV rays.    Patent document 1: Japanese Laid-Open Patent Publication No. 2002-357830